Novel critical role of Toll-like receptor 4 in lung ischemia-reperfusion injury and edema.

Toll-like receptors (TLRs) of the innate immune system contribute to noninfectious inflammatory processes. We employed a murine model of hilar clamping (1 h) with reperfusion times between 15 min and 3 h in TLR4-sufficient (C3H/OuJ) and TLR4-deficient (C3H/HeJ) anesthetized mice with additional studies in chimeric and myeloid differentiation factor 88 (MyD88)- and TLR4-deficient mice to determine the role of TLR4 in lung ischemia-reperfusion injury. Human pulmonary microvascular endothelial monolayers were subjected to simulated warm ischemia and reperfusion with and without CRX-526, a competitive TLR4 inhibitor. Functional TLR4 solely on pulmonary parenchymal cells, not bone marrow-derived cells, mediates early lung edema following ischemia-reperfusion independent of MyD88. Activation of MAPKs and NF-kappaB was significantly blunted and/or delayed in lungs of TLR4-deficient mice as a consequence of ischemia-reperfusion injury, but edema development appeared to be independent of activation of these signaling pathways. Pretreatment with a competitive TLR4 inhibitor prevented edema in vivo and reduced actin cytoskeletal rearrangement and gap formation in pulmonary microvascular endothelial monolayers subjected to simulated warm ischemia and reperfusion. In addition to its well-accepted role to alter gene transcription, functioning TLR4 on pulmonary parenchymal cells plays a key role in very early and profound pulmonary edema in murine lung ischemia-reperfusion injury. This may be due to a novel mechanism: regulation of endothelial cell cytoskeleton affecting microvascular endothelial cell permeability.

In vitro modeling of nonhypoxic cold ischemia-reperfusion simulating lung transplantation.

OBJECTIVE: Although anoxia/reoxygenation of cultured cells has been used to model lung ischemia-reperfusion injury, this does not accurately mimic events experienced by lung cells while a lung is retrieved from a donor, stored, and transplanted. We developed an in vitro model of nonhypoxic ischemia-reperfusion injury to simulate these events. METHODS: Human umbilical vein endothelial cells underwent simulated cold ischemia by replacing 37 degrees C culture media with 4 degrees C Perfadex (Vitrolife, Kungsbacka, Sweden) solution for 5 hours in 100% O(2). Culture dishes were allowed to warm to room temperature for 1 hour (implantation), and then Perfadex solution was replaced with 37 degrees C culture media (reperfusion). RESULTS: During cold ischemia, the human umbilical vein endothelial cell filamentous actin cytoskeleton quickly became rearranged, and gaps developed in the previously confluent monolayer occupying 20% of the surface area. Simulated reperfusion resulted in reorganization to a confluent monolayer. Development of gaps was not due to enhanced necrosis based on lactate dehydrogenase retention assay. Endothelial cytoskeletal rearrangement could account for early edema caused by ischemia-reperfusion injury with reperfusion. Mitogen-activated protein kinase and nuclear factor kappaB activation occurred with simulated reperfusion despite normoxia. Levels of the proinflammatory cytokines interleukin 6 and interleukin 8 were significantly increased in media at the end of reperfusion. CONCLUSIONS: Exposing human umbilical vein endothelial cells to simulated cold ischemia without hypoxia causes reversible cytoskeletal alterations, activation of inflammatory pathways, and elaboration of cytokines. Because this model accurately depicts events occurring during lung transplantation, it will be useful to explore mechanisms regulating lung cell response to this unique form of ischemia-reperfusion injury.